We have previously shown in four separate groups of adult patients with seasonal affective disorder (SAD) that exposing these patients to bright full-spectrum light for 3 hours in the morning and 3 hours in the evening, or for 5 hours in the evening alone, produces marked antidepressant effects. In this past year we examined whether the antidepressant effects are mediated via the photoperiod, i.e., whether they depend on extending the normal daylength or whether they will occur even if the light exposure takes place within normal daylight hours. We treated 7 inpatients with SAD in a crossover design involving two 1-week light manipulations separated by a week off lights. The 2 lighting manipulations both involved 2 3-hour periods of bright (2500 lux) light, separated either by 2 hours of dim light (short skeleton photoperiod) or 9 hours of dim light (long skeleton photoperiod). Based on animal studies we predicted that the latter would have antidepressant effects in our patients but that the former would not. In fact, we found the treatment schedules to be equally efficacious, which would argue against a photoperiodic mechanism for the antidepressant effects of bright environmental light in SAD. We collaborated with Dr. Carla Hellekson in Fairbanks, Alaska, who showed in 6 patients with SAD that two hours of bright light in the morning, two hours of bright light in the evening, and two hours f bright light divided equally between morning and evening were all equally effective in treating patients with SAD. In an uncontrolled study we showed that increasing the environmental light had significant antidepressant effects in 6 children and adolescents with SAD. In further studies we are continuing to explore the formal properties of light treatment in SAD.